The present teachings relate to generating power and power electronics, and more specifically to generating direct current (DC) power.
Electricity generation is traditionally accomplished by large generating plants such as nuclear reactors, hydro-electric dams, coal, and gas fired boilers. The electric power that is generated is stepped up to a higher voltage, the voltage at which it connects to the transmission network. The transmission network can move, i.e. “wheel”, the power long distances until it arrives at a local utility distribution network where, at a substation, the power can be stepped down in voltage from a transmission level voltage to a distribution level voltage. As the power exits the substation, it enters the distribution network. Finally, upon arrival at the service location such as a residential home or commercial user, the power is stepped down again from the distribution voltage to the required service voltage(s).
The traditional grid has limitations including, but not limited to, operational overhead, potential for widespread outages, aging technology, and security vulnerabilities. The traditional grid, along with its regional distinctions, is currently subject to the introduction of more efficient and smarter, although often smaller power generation technologies. Regional and local grids are now subject to low level dispersed power generation from regional large and small wind applications, small hydro-electric facilities, and even commercial and residential photovoltaic installations, for example. As such regional and local power producers come on-line, the characteristics of power generation can, in some new grids, be entirely opposite of those listed herein. The characteristics of regional and local power producers could be attractive for some locales, and can be implemented in the form of what is termed a “smart grid” using a combination of new design options such as net metering, electric cars as a temporary energy source, and/or distributed generation.
Of recent interest is the local generation and distribution of power, in particular, DC power. Many appliances require a conversion from the grid's AC power supply to DC power, which adds to the inefficiencies already inherent in centralized power transmission from large remote power generators. EMERGE® Alliance is an open industry association developing standards for DC power distribution. Current standards include DC power distribution in interiors, and desktop/telecom standards. Alternatively, DC power can be provided to the grid through commercially available inverters, and can be used in local power distribution facilities.
An example of a system that produces DC power is described in U.S. Pat. No. 7,701,705, a free-piston Stirling engine driving an alternator to supply power through a bus to a user load. In this system, the engine is operated at its maximum piston stroke, and the battery is charged if needed, when the bus voltage is in the range between a design nominal bus voltage (V1) and a design minimum battery charging bus voltage (V2). This system could benefit from an efficient means for starting the engine. Exemplary start-up circuits, such as for example, the one described in U.S. Pat. No. 8,957,710, include a detection circuit and a transition circuit for preventing the problem of incapability in transition as well as achieving the purpose of low power consumption. These types of systems lack a means to discontinue current flow to the start-up circuits when the engine is operating.
What is needed is a system to provide DC power from an engine to power a load and to power the control of the system, the system having a relatively small start-up power supply.